Why get that complex? I'd rather:

{
    no strict 'refs';
    for my $method (qw( seconds minutes hours days weeks months years 
+))
    {
        *{ $method }         = sub { return $_[0]->{ $method } };
        *{ 'in_' . $method } = sub { 
            return $_[0]->{ time } / $_[0]->{_table }{ $method } }    
+}       
}   }
[download]

Funny, that ended up quite a bit shorter than I expected.